The use of high intensity discharge (HID) lamps has become increasingly prevalent for several reasons, including their higher output in lumens per watt than incandescent lights, resulting in lower operating costs. The reliability of HID lamp fixtures is another reason for the acceptance of such fixtures for a wide variety of commercial and consumer applications.
HID lights are increasingly being used in cold climates and other low temperature applications. Mercury vapor and high pressure sodium HID lights are typically suitable for temperatures down to minus 20 degrees Celsius, or minus 4 degrees Fahrenheit. Below that temperature, HID light fixtures typically exhibit one or more problems, including malfunction of the thermal photocell that is often used to turn the light on at dusk and off at dawn, and unreliable firing even if the photocell operated properly.
Temperatures in northern parts of the United States, in Canada, in other parts of the world, and in artificially controlled environments (e.g. storage freezers) often reach below the limits of such typical HID light fixtures.
It is therefore desirable to provide a means for reliably operating a HID light fixture at lower temperatures than is typically possible with existing HID light fixtures.